Hardfacing is a way of modifying the surface of a component to withstand abrasion.
The most common grades of weld metal for hard facing are the Martensitic 300 and 600 Hv steels. The 300 is used when the component is to be machined or as an intermediate layer before the 600 hardness. The 600 is basically as hard as it gets but you will see weld metals claiming 1000Hv. These are hard particles in a softer matrix.
One of the best hard facing alloys contains 25 -30 %Cr with 4 - 5% Carbon which gives a very abrasion resistant overlay which is also quite ductile. Its probably worth paying that bit more as it will last a lot longer than the 600Hv alloy. It is especially good for ploughs and digger buckets. This grade is often called Chromium Carbide grade and is typically shown as having a hardness of 60 Rockwell C (Rc).
Hardfacing in cross patterns on the jaws of a crusher (Flynns Buckets)